Questions to which we address our emphasis in this application are the control mechanisms regulating the commitment of hemopoietic stem cells and maturation of early hemopoietic precursors. Specifically, is this commitment process under influences of external factors or genetically predetermined? What are the factors regulating the proliferation and maturation of early committee hemopoietic precursors? Studies will be done using clonal cell culture techniques for granulopoietic and erythropoietic precursors. Assay techniques for human stem cell function are not available. Considering the recent progress in primary cell culture of murine hemopoietic cells and development of apparent murine stem cell culture assays in our laboratory, we believe attempts to develop a cell culture method for human hemopoietic stem cell function is justified. As a practical application to these studies, we proposet to examine the potential use of human cadaveric marrow cells.